Semiconductor device

2. The semiconductor device according to claim 1, wherein a surface of the base is a (0001) surface.

3. The semiconductor device according to claim 1, wherein a composition of the second nitride semiconductor at a surface in contact with the contact layer is represented by Alx1Ga1-x1N where 0.00≤x1≤0.20.

4. The semiconductor device according to claim 1, wherein the third nitride semiconductor and the fifth nitride semiconductor include Ga.

5. The semiconductor device according to claim 1, wherein the third nitride semiconductor and the fifth nitride semiconductor are GaN.

6. The semiconductor device according to claim 1, wherein a composition of the fourth nitride semiconductor is represented by Iny2Alx2Ga1-x2-y2N where 0.00≤x2≤1.00 and 0.00≤y2≤0.20.

7. The semiconductor device according to claim 1, wherein a thickness of the channel layer is 50 nm or less.

8. The semiconductor device according to claim 1, wherein the fifth nitride semiconductor contains an n-type impurity at a concentration of 1×1017 cm−3 to 5×1020 cm−3.

9. The semiconductor device according to claim 1, wherein the fifth nitride semiconductor contains Si, Ge, or O or any combination of Si, Ge, and O as an n-type impurity.

12. The semiconductor device according to claim 1, wherein a portion of the buffer layer below the contact layer is thinner than a portion of the buffer layer below the channel layer.

13. An amplifier comprising the semiconductor device according to claim 1.

14. A power supply apparatus comprising the semiconductor device according to claim 1.